Recessed screw heads and drivers

ABSTRACT

A screw head is provided with projections on selected of the driver-engageable surfaces of the head to interlock with surfaces and edges of the driver to reduce the tendency for the driver to slip out of the recess during driving and also to provide a temporary stick-fit between the driver and the recess.

This is a division of application Ser. No. 505,324 filed Sept. 12, 1974now U.S. Pat. No. 4,084,478 dated Apr. 18, 1978.

BACKGROUND OF THE INVENTION

This invention relates to improvements in fasteners generally and inparticular to screws or the like having recesses which are suited to bedriven with powered drivers. Among the primary difficulties which havebeen presented in connection with the driving of screws has been tocontrol the torque to which such screws are tightened by the driver. Thedifficulties are amplified when power drivers are used. Prior to thedevelopment of power drivers with clutch devices, which may be preset tocontrol the torque applied to the screw, the most widely used techniquefor controlling the torque was to design the shape of thedriver-receptive recess and the driver so that they would disengage whena predetermined torque was reached. For example, U.S. Pat. No. 2,046,837to Phillips shows such a recess in which the walls of the recess areinclined so as to impart an axial removal force to the driver as theapplied torque increases, a characteristic referred to as "cam-out".While this was generally effective, it required some measure of skill bythe operator in that in order for the driver to cam-out of the recess atthe desired torque, the operator would have to control the amount ofaxial force of the driver and would also have to maintain the drivingtool in substantially axial alignment with the screw. Because of theoperator-controlled variables, it was not uncommon for power drivenscrews to be over-torqued or under-torqued. In addition, disengagementof the driver would cause the driver to slip out of the recess andsometimes mar the surface of the work.

With the development of improved clutches for power drivers to set andcontrol the maximum applied torque, it became desirable to provideimproved recesses which could be engaged by the driver more firmly toretard further the tendency to cam-out. To this end, efforts were madeto design the driver-engaged driven surfaces of the recess so that theywould be as vertical (parallel to the screw axis) as possible to avoidthe camming effect of upwardly and outwardly inclined drive walls. Forexample, U.S. Pat. Nos. 3,237,506 and Re. 24,878 illustrate recesseshaving substantially vertical drive walls.

While a recess having vertical drive walls is generally effective toretard cam-out along the axis of the screw when the driver is in axialalignment with the axis of the screw, there still is a tendency for thedriver to slip out of engagement from the recess when the driver is outof axial alignment with the screw. This results from the fact that whenthe driver axis is out of alignment with the screw axis, the surfaces ofthe driver become inclined with respect to the recess surfaces which,when the screw is driven tends to urge the driver out of the recess.Thus, a certain degree of skill still is required even when using apower driver having a slip clutch in that the driver must be maintainedin axial alignment with the screw in order to fully achieve the benefitsof the vertical walled recess. However, even skilled operators, byreason of fatigue or for other reasons, sometimes may have difficulty inmaintaining the driver and screw in axial alignment. It is among theobjects of the invention to provide an improved recess configurationwhich retards the tendency of the driver to pop-out of or otherwisebecome disengaged from the screw recess even when there is somemisalignment between the driver and the screw.

Also among the prior considerations relating to recessed screws is thecharacteristic which is commonly referred to as "stick-fit", a conditionin which the recess and driver fit together so that the screw will clingto the driver when they are mated. This is desirable in those instanceswhere it is an advantage to the operator to attach the screw to thedriver so that he may then position the screw by the driver and thensimply drive the screw into the workpiece. Such a stick-fit often isdifficult to achieve with consistency because of variations inmanufacturing tolerances. Also, drivers and recess-forming punches wearwith use which may result in somewhat less than an ideal stick-fitbetween a particular screw and driver. Moreover, there are instances inwhich, while a stick-fit is an initially desirable characteristic, itmay become undesirable if the fit is so tight that it tends to maintainthe stick-fit after the screw has been driven. In this regard, manydrivers hold the driver bit in a socket by a magnet which, if the stickfit is retained after the screw has been driven, results in the bitinconveniently remaining stuck to the screw after it has been driven asthe magnets employed usually retain the bit only under a light force. Itis among the objects of the invention to provide a screw recess havingstick-fit characteristics and in which the force employed in driving thescrew deforms those regions of the recess which provided the stick-fit,thus destroying the stick-fit and assuring easy removal of the driverbit.

SUMMARY OF THE INVENTION

In brief, the invention resides in the provision of one or morelongitudinal ribs formed on the drive and/or back out walls of the screwrecess. Each of the ribs extends along a direction which lies generallywithin a plane parallel the axis of the screw. Each rib projectsslightly from the surface of the recess wall into the recess so thatwhen the driver is inserted into the recess it will be engaged by theribs under a light but sufficient force to enable the screw to cling tothe driver. The ribs are dimensioned and located so that even when thedriver is out of axial alignment with the screw (as is not infrequentlythe case) some of the edges of the blade or blades of the driver willdig into the ribs and interlock therewith to retard disengagement of thedriver as long as the rotary driving force is applied. The ribs areintegral with and are made from the same metal as the screw whichtypically is softer than that of the driver and will deform under theinfluence of the driving force. After the screw has been driven, andbecause the ribs have been deformed during the driving, the stick-fit isminimized or destroyed and the driver can be removed easily and withoutdifficulty.

The driver may be of conventional construction to mate with theparticular recess. In alternate embodiments of the invention, the drivermay be modified to provide transversely extending ribs on selectedregions thereof which will interlock with the ribs on the recess toenhance the grip therebetween.

It is among the objects of the invention to provide an improved screwrecess which retards premature disengagement of the driver from therecess.

Another object of the invention is to provide an improved screw recessin which the driver engaging surfaces thereof are provided with one ormore longitudinal ribs which extend outwardly of the recess surface.

Another object of the invention is to provide an improved recess of thetype described in which the ribs are deformable and can interlock withselected regions of the driver.

A further object of the invention is to provide a recess which willreceive the driver in a stick-fit yet which will not tend to cling tothe driver after the screw has been driven.

Still another object of the invention is to provide an improved driverhaving ribs formed at selected locations thereof for interlockingengagement with a screw recess.

Another object of the invention is to provide a screw having a recess inwhich precise conformity of the driver with the recess is not requiredfor optimum performance.

DESCRIPTION OF THE DRAWINGS

The foregoing and other objects and advantages of the invention will beunderstood more fully from the following further description thereof,with reference to the accompanying drawings wherein:

FIG. 1 is an elevation of a recessed head screw and driver in a matedconfiguration;

FIG. 2 is a plan illustration of a recessed head screw modified toinclude ribs pursuant to the invention with the ribs shown in enlargedexaggeration for clarity;

FIG. 2A is an enlarged plan illustration of a portion of the recessshown in FIG. 2 and illustrating, in enlarged exaggeration, the rib inaccordance with the invention;

FIG. 3 is a sectional elevation of the recess as seen along the line3--3 of FIG. 2;

FIG. 4 is a plan view of the recess of FIG. 2 mated with a driver assuggested in FIG. 1 with the driver being shown in section at the top ofthe screw as suggested by line 4--4 in FIG. 1;

FIG. 5 is a fragmented illustration of the recess of FIG. 2 inengagement with a driver but with the driver axis being misaligned withrespect to the screw axis;

FIG. 6 is a plan view of the recess and driver in the configuration ofFIG. 5 with the driver being shown in section at the top surface of thescrew as suggested by the line 6--6 in FIG. 5;

FIG. 7 is a somewhat diagrammatic illustration of the relationshipbetween one of the driver blades and its recess groove as seen along theline 7--7 of FIG. 6;

FIG. 8 is an illustration of another of the driver blades similar toFIG. 7 and as seen along the line 8--8 of FIG. 6;

FIG. 9 is a plan view of the recess shown in FIG. 2 further modified toinclude the ribs, in enlarged exaggeration, of the invention on thedrive walls and back out walls of the recess grooves.

FIG. 10 is an illustration similar to FIG. 7 and illustrating therelationship between a misaligned driver blade and the recess grooveconfiguration shown in FIG. 9;

FIG. 11 is a side elevation of a modified form of driver which may beemployed in connection with the invention;

FIG. 12 is an end view of the driver of FIG. 11;

FIGS. 13-15 are somewhat diagrammatic illustrations taken in sectionthrough a combined recess groove and the blade of a driver shown in FIG.11 and illustrating the cooperation between the recess groove and themodified driver blade;

FIG. 16 is a side elevation of a further modified driver;

FIG. 16A is an illustration of still another modified form of driverblade;

FIG. 17 is a sectional illustration of a driver blade as seen along theline 17--17 of FIG. 16A;

FIG. 17A is an illustration similar to FIG. 17 and showing a variationof the configuration shown in FIG. 17;

FIG. 18 is an illustration similar to FIG. 17 showing a furthervariation thereof;

FIG. 19 is a side elevation of a driver blade embodying a furthervariant of the invention;

FIG. 20 is a sectional illustration of the variant of FIG. 19 as seenalong the line 20--20 of FIG. 19;

FIG. 21 is a side elevation of still another modification of theinvention;

FIGS. 22-24 are illustrations of further configurations for the driveand/or back out walls of the recess grooves;

FIG. 25 is a somewhat diagrammatic sectional elevation, similar to thatof FIGS. 7 or 8, illustrating the phenomenon of fall away in a coldformed recess groove;

FIG. 26 is a fragmented illustration of a combined recess screw anddriver in which the screw has a significant amount of fall away;

FIG. 27 is an illustration of one blade of a driver which may beemployed advantageously with screws having significant amounts of fallaway;

FIG. 28 is an illustration of a modified form of driver havingrecess-engaging ribs at locations between the driver blades;

FIG. 29 is a fragmented sectional illustration of a portion of thedriver of FIG. 28 as seen along the line 29--29 of FIG. 28;

FIG. 30 is an illustration similar to FIG. 29 showing an alternative tothe structure shown in FIG. 29;

FIG. 31 is an illustration of a recess having a rib included therein inaccordance with a further aspect of the invention in which the rib isdisposed at that portion which defines the central portion of therecess;

FIG. 32 is a plan view of the configuration shown in FIG. 31;

FIG. 33 is an illustration of a further variant of the driver shown inFIG. 28;

FIG. 34 is a plan view of a recess having inclined sidewalls and beingprovided with ribs in accordance with another aspect of the invention inwhich the ribs taper downwardly with respect to the groove walls fromwhich they protrude, the ribs being shown in enlarged exaggeration;

FIG. 35 is an enlarged plan illustration of one of the recess grooves ofFIG. 34;

FIG. 36 is an illustration of the recess shown in FIG. 35 as seen alongthe line 36--36 of FIG. 35;

FIG. 37 is an illustration of the recess groove shown in FIG. 35 as seenalong the line 37--37 of FIG. 35;

FIG. 38 is an illustration similar to FIG. 36 and showing a furthervariation in the configuration of the rib;

FIG. 39 is a plan view of the invention as incorporated in another typeof recess with the ribs shown in enlarged exaggeration;

FIG. 40 is a sectional elevation of the recess shown in FIG. 39 as seenalong the line 40--40 of FIG. 39;

FIG. 41 is a sectional elevation of the recess of FIG. 39 as seen alongthe line 41--41 of FIG. 39;

FIG. 42 is an illustration similar to FIG. 41 showing a modified ribwhich is inclined downwardly and inwardly;

FIG. 43 is an illustration of the rib configuration of FIG. 42 as seenin plan;

FIG. 44 is an illustration of the invention as incorporated in stillanother type of recess;

FIG. 45 is an illustration of the recess shown in FIG. 44 as seen alongthe line 45--45 of FIG. 44;

FIG. 46 is an illustration of the recess shown in FIG. 44 as seen alongthe line 46--46 of FIG. 44;

FIG. 47 is an illustration similar to FIG. 45 showing a further variantof the rib configuration;

FIG. 48 is an elevation of a back out wall of the recess of FIG. 44 asseen along a direction suggested by the line 48--48 of FIG. 44 andmodified to include ribs in accordance with the invention;

FIG. 49 is an elevation of a conventional driver used in connection withthe recess shown in FIG. 44;

FIG. 50 is an end view of the driver of FIG. 49;

FIG. 51 is a side elevation of the driver of FIG. 49 modified to includea configuration of ribs in accordance with one aspect of the invention;

FIG. 52 is a side elevation of a portion of the driver of FIG. 49showing a further variation in the rib configuration on a driver blade;

FIG. 53 is a side elevation of a further embodiment of the d-riber;

FIG. 54 is a side elevation of a portion of the driver showing the backout wall and the manner in which it may be hollowed out to engage therecess;

FIG. 55 is an illustration as seen along the line 55--55 of FIG. 54;

FIG. 56 is a side elevation of a protruding head for a screw fastenermodified to include the invention; and

FIG. 57 is a plan view of the fastener shown in FIG. 56 andillustrating, in section, the manner in which the head is engaged by anappropriate driving tool.

FIG. 58 is an end view of a punch which may be employed to fabricate therecess shown in FIGS. 2 and 3;

FIG. 59 is a side elevation of the punch shown in FIG. 58;

FIG. 60 is an end view of a punch which may be employed to fabricate therecess shown in FIGS. 34-36;

FIG. 61 is a side elevation of the punch shown in FIG. 60;

FIG. 62 is an end view of a punch which may be employed to fabricate therecess shown in FIGS. 31 and 32; and

FIG. 63 is a side elevation of the punch shown in FIG. 62.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a combined recessed screw 10 and driver 12 with the driverseated ideally in the recess and in axial alignment with the screw.While the particular recess and driver shown is that described in U.S.Pat. No. 2,474,994 to Tomalis the principles of the invention may beemployed with other types of recesses and screw head configurations, aswill be apparent. FIGS. 2 and 3 illustrate the Tomalis recess modifiedto include one form of the present invention. The recess in thisembodiment shown is of polygonal form and may be defined as generallycruciform in plan. The recess includes a central portion 14 and aplurality of grooves 16 radiating outwardly from the center portion 14.The grooves 16 are separated from each other by downwardly and inwardlyinclined recess intermediate walls 18. The bottom regions of the grooves16 and walls 18 merge into a generally concave recess bottom 20. Each ofthe grooves 16 is defined by a pair of triangular sidewalls 22, 22' andan end wall 24 which is inclined downwardly and inwardly. In the Tomalisscrew illustrated, the groove sidewalls 22, 22' also are inclined but ata compound angle in which the planes of the sidewalls 22, 22' convergeboth in a downward and in an inward direction as defined more fully inthe Tomalis patent. In the following description of the invention thescrew and recess will be considered as right handed, in which sidewall22 would be considered to be the driving wall when the screw is beingfastened and in which the opposite sidewall 22' (the back out wall) willfunction as the driving wall when the screw is being removed.

In accordance with the invention, the driving walls 22 of the recessgrooves 16 are provided with longitudinal ribs 26. In the embodimentshown in FIGS. 2-7 the ribs 26 extend from the intersection of the drivewall 22 and end wall 24 of the groove upwardly toward the intersectionof the top 27 of the screw head with the drive wall 22. Theconfiguration and number of ribs 26 is subject to a number ofvariations, as will be described. In this configuration shown the rib 26is of generally triangular cross-sectional shape having an apex or ridge28 and sidewalls 30 which merge with the drive wall 22 (see enlargedFIG. 2a). The rib 26 extends the full height of the drive wall 22 and islocated at the radially inward region of the drive wall 22, in proximityto the juncture of the drive wall 22 and the intermediate wall 18. Therib 26 protrudes from the drive wall 22 just slightly, for example, ofthe order of a few thousandths of an inch or less, depending on the sizeof the fastener, the illustration of the ribs herein being highlyexaggerated for purposes of illustration. The apex 28 of the rib 26faces inwardly toward the groove 16 and substantially parallels theplane of drive wall 22. The rib also extends along a direction whichgenerally lies within a plane parallel the screw axis. In the embodimentshown in FIGS. 2 and 2A the sidewalls 30 lie generally in planes whichdo not parallel the screw axis and when viewed from the axis of thescrew, as in FIGS. 2 and 2A, the surfaces of the rib sidewalls 30 willbe exposed. As will be described with regard to other embodiments of theinvention, the sidewalls of the rib 26 may be formed to lie in planeswhich do substantially parallel the axis of the screw, in which case theridge 28 will also parallel the screw axis. In the embodiment shown inFIGS. 2 and 2A, however, where the sidewalls 30 are inclined asdescribed, the ridge 28 will also be disposed generally askew to thelongitudinal axis of the screw so that the rib 26 may receive the bladeof the driver in a wedged fit.

As shown in FIGS. 1, 4 and 6 the driver may be of conventional designhaving a shank 32 and a bit formed at the end of the shank, the bitbeing generally complementary to the recess. The bit is formed to defineblades 34 which extend from a central core 33 and are equal in numberand spacing to the grooves 16 in the screw recess. Between each pair ofadjacent blades 34 the core 33 of the driver bit is defined byintermediate walls 36 generally complementary to the intermediate walls18 of the recess. The bottom 38 of the driver may be formed with agenerally conical tip similar in shape to the bottom 20 of the recess.

It may be noted that in the recess and driver described in the Tomalispatent a "stick-fit" characteristic is achieved by dimensioning theintermediate walls 36 of the driver and intermediate walls 18 of therecess so that when fully mated they engage in a close, wedging fitwhile the thickness of the driver blades 34 is slightly less than thewidth of the recess grooves. While under ideal manufacturing conditionsthe Tomalis recess and driver may be formed to achieve the desiredwedging effect, the more usual manufacturing conditions often result ina recess-driver fit which is less than ideal. For example, as the punchemployed in cold forming the recess wears from use, the resulting recessmay not receive the driver in the intended manner and may not perform asintended. Also contributing to the difficulties encountered with theTomalis recess is the phenomenon sometimes referred to as metal"fall-away" in which the upper regions of the groove sidewalls, as theyapproach the top surface of the screw head tend to curve outwardly andaway from their intended location. This results in a progressivelyenlarged recess configuration near the upper portions of the recesswhich contributes to premature disengagement of the driver with therecess, particularly when the driver is slightly out of axial alignmentwith the screw.

By providing the recess with the ribs 26 in accordance with theinvention, the above difficulties may be reduced materially. The ribs 26are dimensioned to project into their respective grooves 16 so that theywill present a slight interference with the blades 34 of the driverwhich are inserted into the recess grooves. Because the ribs 26 are ofrelatively small cross-sectional dimensions they enable the screw headto be manually applied onto the end of the driver in the desiredstick-fit. The ribs 26 will perform their intended function even where aparticular screw exhibits a substantial degree of metal fall-away. Suchfall-away usually is confined to the upper portions of the screw recess.Where the ribs 26 extend downwardly to the bottom of the drive wall 22,at least the lower portions of the ribs 26 will be properly located toengage the driver blades 34 and cling to them. When the screw is driven,the force of the driver blades 34 against the slightly projecting ribs26, particularly at the end of the driving procedure where theresistance to torque is substantially increased, deforms the ribs 26which are quite small and deformable in relation to the strength of thedriver. The ribs 26 deform to an extent sufficient to destroy thestick-fit characteristic thus enabling the driver to be withdrawn easilyand without any tendency to remain stuck to the screw.

The manner in which the ribs 26 retard the tendency for the driver todisengage from the recess during driving when the driver and screw areslightly misaligned may be seen from FIGS. 5-8. FIG. 5 is a fragmentedillustration of a combined recess and driver in which the driver axis 40is slightly misaligned from the screw axis 42 as suggested by the angleA. The driver also is slightly withdrawn from the recess as is typicallythe case when the driver and screw are misaligned. FIGS. 5 and 6illustrate the relationship of the driver and recess when themisalignment is directly to the right of the recess axis as seen inthose figures and as suggested by arrow 44 in FIGS. 5 and 6. When thiscondition occurs with the screw being driven in a clockwise direction,the primary contact between the driver and recess occurs between driverblades 34a and 34c with their respective grooves. Driver blades 34b and34d, which lie generally along the direction of misalignment of thedriver, effect little, if any, significant grip on any of the surfacesof their respective recesses. Thus, as shown in further exaggeration inFIGS. 7 and 8, the primary regions of contact between each of the driverblades 34a, 34c and their grooves will be at the region of engagementbetween the lower portion of one side of each of the driver blades 34a,34c with one sidewall of the recess groove and the other region ofcontact will be between the upper portion of the opposite surfaces ofthe blades 34a, 34c with a more upwardly disposed portion of theopposite sidewall of their grooves. As seen in FIG. 7 the lower portionof the driving surface 46 of blade 34a will bear toward the driving wall22 of its groove 16 which will cause the lower edge 48 of the blade 34ato dig into the rib 26 on the wall 22. This engagement of the driverblade with the rib results in an interlocking between the two whichtends to retard further withdrawal of the driver from the recess.

As the rotation of the screw is continued but with the attitude of axialmisalignment remaining the same it will be seen that as the blades 34approach a further rotation of 90°, blade 34a will progressivelydecrease its engagement with its associated rib 26 while blade 34dprogressively shifts to a more misaligned attitude in its respectivegroove, to the angle of misalignment A between the driver and screw. Asblade 34d is progressively rotated to the misaligned attitude within itsrecess the lower edge 48 of blade 34d progressively digs into andinterlocks with the rib 26 associated with that groove. Thus, as thescrew is driven, the blades 34 successively dig into and release fromthe ribs 26 and in a manner which continually retards the tendency ofthe misaligned driver to be urged out of the recess. It also retards thetendency for the angle of misalignment to be increased.

With regard to the embodiment described thus far it may be noted thatwhile blade 34c is canted within its recess groove (FIG. 8) itsinclination with respect to the drive wall 22 is reversed from that ofblade 34a, so that the driving surface 46 of blade 34c will engage theupper region of the rib 26 in that groove. While this may tend toflatten out the upper region of the rib it will not enable blade 34c todig into the rib. In order to enhance the overall grip between themisaligned driver and the recess, it may be desirable to provide a rib26' on the other, back out wall 22' of the groove 16 as shown in FIGS. 9and 10. Thus, when a blade 34 is in the position of blade 34c, the loweredge portion 48' of the blade will engage the rib 26' on the back outwall 22'. Thus, the blades in the positions of blades 34a and 34c eachwill contribute to retarding of withdrawal of the misaligned driver fromthe recess when in the configuration shown in FIGS. 5 and 6.

The foregoing cooperation between the driver and recess may be enhancedfurther by providing a driver in which selected of the recess engagingsurfaces of the blades are formed to increase the interlocking effectbetween the blades 34 and the ribs 26. FIGS. 11 and 12 show a modifieddriver in which the blades 34 include ribs 50 formed on the lowerregions of their driving faces 46. The driver ribs 50 may extendgenerally transversely of the axis of the driver as shown and, ingeneral, the driver ribs 50 should extend along a direction such thatwhen the driver blades 34 are inserted into the recess grooves 16 thedriver ribs 50 will cross and intersect with the ribs 26 on the recessdrive walls 22. The driver and its ribs 50 which typically are made froma harder metal than that from which the screw and its ribs 26 are madewill cause the driver ribs 50 to cross and dig into the recess ribs 26under the influence of the applied torque as suggested somewhatdiagrammatically in FIG. 13. If the driver and screw are axiallymisaligned, the driver ribs 50 may aid in digging into the recess ribs26 as suggested in FIG. 14 which provides a somewhat better interlockbetween the blade and the rib 26 than that as suggested in FIG. 7. Thedriver may also include at least one additional driver rib 50a on thedriving face 46 of the blade 34 so that in the event of a misaligneddriver and screw, a blade in the position of blade 34c in FIG. 6 will beable to engage and dig into the upper region of the recess rib 26 assuggested in FIG. 15.

Where the recess groove is provided with ribs 26, 26' on each of thegroove walls 22, 22', as suggested in FIGS. 9 and 10, the driver alsomay be provided with transverse blade ribs 50a, 50a' on both of itsdriving and back out surfaces as suggested in FIG. 16. In some instancesit may be desirable to provide one or more additional ribs on the driverblades intermediate the ribs 50, 50a and 50', 50a'. It should be noted,however, that the number of ribs on each surface of the driver blades 34preferably should not be too great in number or too closely spaced asthis would tend to reduce the ability of the driver ribs 50 and/or 50ato deform and interlock with the recess ribs 26.

The principles described above with regard to the provision of ribs onthe driver blades may be employed with other configurations. Forexample, as shown in FIGS. 16A and 17 a rib 52 may be provided along thelower edge of the blade 34. The rib 52 may be in the form of aprojection as shown more clearly in FIG. 17 or may be formed effectivelyby hollowing the lower region of the face 46 of the driver blade assuggested at 54 in FIG. 17A to leave a relatively sharp rib 52 extendingtherefrom. FIG. 18 is an illustration similar to FIG. 17 but showingthat ribs 52 and 52' may be formed on each lower edge 48 of each driverblade. Moreover, in some instances it may be desirable to providefurther ribs in addition to the edge rib, as suggested in FIG. 19 inwhich a second rib 52a is formed parallel to the first edge rib 52. Theribs 52, 52a may be formed on each side of the blade as suggested at52', 52a' in FIG. 20. FIG. 21 illustrates a further variation in which aplurality of driver ribs 52, 54 are provided on the face or faces of theblades and which they extend along different directions which neitherparallel each other or the axis of the driver.

Still further modifications may be made with respect to the use of theribs 26. For example, in some instances it may be found thatsatisfactory results are obtained when the rib does not extend fully tothe top of the sidewall 22, or 22' of the groove but, instead,terminates before it reaches the upper end as suggested in FIG. 22.Additionally, there may be instances in which it is found to bedesirable to employ a plurality of ribs 26 on either or both of thesidewalls 22, 22' of the recess grooves as suggested in FIG. 23 whichshows a plurality of such ribs 26 in which the upper ends of the ribslie generally along a line which parallels the end wall 24 of theparticular recess groove 16. FIG. 24 shows a further variation in whichthe recess sidewall has a plurality of ribs 26 and in which each rib 26extends fully from the bottom to the top of the sidewall.

The phenomenon of metal fall-away, referred to above, results in a screwhaving an imperfect recess, the degree of imperfection depending in parton the extent of metal fall-away. FIG. 25 is a sectional elevation of arecess groove as seen in a manner similar to FIG. 7 or 8 butillustrating the effect of metal fall-away and the resulting grooveconfiguration. As can be seen, the upper regions of the walls 22, 22' donot merge with the top surface of the screw in a well defined manner butinstead, fall outwardly and away from their intended location (indicatedin phantom at 57 in FIG. 25) with the result that a substantial portionof the upper regions of the walls flare upwardly and outwardly, ingenerally arcuate configuration. Recesses having a substantial amount offall-away have an adverse effect on the functioning of the recess inthat they provide a reduced driving wall area. In addition, because ofthe arcuate flared surface at the upper region of the recess wall,fall-away results in a more wobbly fit between the recess and the driverwhich, in turn, increase the tendency for the driver to becomemisaligned and cam-out or otherwise pop out of the recess. As may beseen from the fragmented illustration in FIG. 26 when the driver andscrew are misaligned and with the driver partly withdrawn from therecess, the outer face 56 of the blades (here blade 34d) may bearagainst the outer top edge 58 of its associated recess groove. Thisresults from the fact that the misalignment is not limited by engagementof the opposite drive and back out faces 46, 46' of the blades 34a, 34cwith their respective recesses as was shown in FIG. 5, because the upperregions of the sidewalls 22, 22' have fallen away and cannot engage theupper portions of faces 46, 46' of the driver blades. When thissituation is presented, the primary contacting regions between themisaligned driver and recess will be at the lower region of the drivingface 46 of blade 34a with drive wall 22 of its recess, the lower regionof back out face 46' of blade 34c with the back out wall 22' of itsassociated recess and the end wall 56 of blade 34d with the upper region58 of end wall 24 of its associated groove. In order to effect a morefirm grip between the misaligned driver and screw, the end wall 56 ofthe driver blade may be formed to define serrations 60 (see FIG. 27)which can engage and effect somewhat of a grip on the upper portion 58of the recess end wall 24.

It sometimes occurs that when the driver and screw are misaligned andwith the driver slightly withdrawn from the recess, the primary pointsof contact between the driver and recess are not between the driverblades 34 and recess grooves 16 but are, instead, between theintermediate driver walls 36 and corresponding intermediate walls 16 onthe screw. While this condition is more likely to occur when aparticular screw has a significant amount of fall-away, it also mayoccur with a satisfactorily formed recess such as that shown in FIGS. 2and 3 when the driver is misaligned and when the screw has been rotatedapproximately 45° from its orientation shown in FIG. 6 to the positionsuggested in phantom at 16' in FIG. 6 (i.e., the screw recess is in aposition in which the direction 44 of misalignment generally bisects apair of adjacent engaged driver blades and recess grooves). In order toresist further the tendency of the misaligned driver and recess todisengage when in this temporary attitude, the driver may be modified atthe lower regions of its intermediate wall 36. The lower portion of thewall 36 is formed to define a rib 64 or protrusion which extendssubstantially fully along the length of its lower edge 62, from thelower end of the driver surface 46 of one of the blades 34 to the lowerend of the back out surface 46' of the next adjacent blade 34. When thedriver and screw are in the configuration described the rib 64 at thelower end of the driver wall 36 will be urged against the lower regionsof the recess intermediate wall 36 and will tend to effect a griptherebetween, further retarding the tendency of the driver to disengagefrom the recess when in this configuration. The rib 64 may be formed ina variety of ways, including, for example, the hollowing out of thelower portion of the driver wall 36 as shown in FIG. 30. The hollowedout portion 66 may be made in a manner which will leave a relativelysharp edge 68 at the lower edge 62 of the driver wall 36 which willfurther tend to dig into the wall 18 of the recess. The recess itselfmay be modified as suggested in FIGS. 31 and 32 by forming it to includea rib 70 which is formed on its intermediate wall 18, the rib 70extending from the bottom of the wall 18, where it meets the recessbottom 20, upwardly toward the top of the wall 18. The rib may extendfully to the top of the wall 18 as shown or may terminate below the topof the wall 18. The rib 70 should lie in a substantially vertical plane(one which parallels or coincides with the longitudinal axis of thescrew).

In addition to providing a rib 64 or sharp edge 68 at the lower edge 62of the driver intermediate wall 36, the more upwardly disposed surfacesof driver wall 36 also may be provided with a rib 64a as suggested inFIG. 33. When the screw is in the 45° rotated position described above,it may thus engage the walls 18 on one side of the recess at their lowerregion and at the upper region of the walls 18 on the opposite side ofthe recess. Where ribs 64a are provided on the upper regions of thedriver intermediate walls 36 it is preferred to employ recess wall ribs70 which extend fully to the top of the recess so that the ribs 64a mayengage the upper ends of the recess ribs 70. The driver ribs 64a shouldbe located on the driver such that they will be below the top surface 27of the screw even when slightly withdrawn from the recess.

Still further modifications may be made to the recess ribs 26 describedabove. For example, in the foregoing description the ribs 26 were shownas being of substantially uniform cross-sectional configuration andhaving a ridge 28 extending substantially parallel to the plane of therecess sidewall from which the ribs project. In some instances, however,it may be desirable to modify the configuration of the rib as shown inFIGS. 34-36 in which the rib 72 has an edge 74 which substantiallyparallels the axis of the screw. In this variation the generallytriangular cross-sectional area of the rib increases in an upwarddirection when the groove sidewall from which the rib extends isinclined upwardly and outwardly. Alternatively, it may be desirable insome instances to employ a rib 76 of a configuration in which its ridge78, as shown in FIG. 38 is neither parallel to the screw axis nor to thesidewall plane but still lies within a substantially vertical plane. Inthis embodiment, the height of the rib 76 as measured from the plane ofits associated sidewall would be intermediate that of the ribconfiguration shown in FIGS. 34-36 and the rib configuration describedwith regard to the embodiment shown in FIGS. 2 and 3.

While the various aspects of the invention have been described thus faras being employed primarily in connection with a recess of the Tomalistype having inclined groove sidewalls, they may also be employed withother recesses. For example, FIG. 39 shows, in plan, a type of screwrecess which is commercially available and which is described more fullyin U.S. Pat. No. Re. 24,878 to Smith et al. In general, that recessincludes a central portion 80 and a plurality of grooves 82 extendingoutwardly from the central portion 80 with each of the grooves beingdefined by a downwardly and inwardly inclined end wall 84 andsubstantially vertical driving and back out walls 86, 88. This recessmay be modified in accordance with the invention by forming it to alsoinclude vertical ribs 90 on either or both of one or more of the drivingor back out walls 86, 88 as suggested in FIGS. 39-41. As shown the ribs90 are of substantially uniform cross-section, generally triangular,having a pair of sidewalls 92 which meet at an apex 94. Each rib 90extends along a direction which lies substantially along a generallyvertical plane. The rib 90 extends from the bottom of the sidewall andmay terminate at the upper edge of the sidewall or, if desired, somewhatbelow the upper edge of the sidewall. In addition, it may be founddesirable in some instances to form the ribs 90 so that they taperupwardly as suggested in FIGS. 42 and 43 from which it may be seen thatthe cross-sectional area of the rib diminishes in an upward direction.The ribs 90 are effective to provide a stick-fit in cooperation with thedriver as described above. It may be noted that here, as in thepreviously described embodiments, the relative dimensions of the rib,particularly the extent to which they protrude from their substantiallyvertical sidewall of the groove is exaggerated substantially in thedrawings for clarity. It is intended that the ribs extend just veryslightly from the sidewall with which they are associated, for example,of the order of a few thousandths of an inch, just enough to enable theribs to cling to the engaged surfaces of the driver. The ribs aredimensioned so that they may be deformed under the increasing torque ofthe driver to destroy the stick-fit characteristic as described.

A commercially available variant of the recess described in U.S. Pat.No. Re. 24,878 is that shown in FIGS. 44-46 which has three grooves 96extending outwardly from the central portion 98 of the recess. While thefour-grooved recess shown in FIG. 39 displays relatively little tendencyto disengage the driver, the three-grooved variant of the recesssometimes presents a tendency for the driver to rock out or spin out ofthe recess, particularly with smaller sized screws. This recess, too,may be modified to include the advantages of the invention by formingthe recess to include a longitudinal rib 100 on at least one of thesidewalls as suggested in FIGS. 44-46 to provide the stick-fitcharacteristic which, while desirable with this recess, has not beenreadily achievable. Should it be desired to modify the three-groovedrecess to retard the tendency of the driver to disengage from therecess, one or more such ribs 100 may be provided in association with atleast one of the sidewalls of each of the grooves. Thus, as shown inFIGS. 44-46 the driving wall 102 of each of the grooves 96 may beprovided with at least one rib 100 which is disposed preferably near theinner regions of the driving wall 102. The ribs 100 extend from thebottom of the sidewall 102 upwardly toward the intersection of thesidewall and the top surface 104 of the screw. If desired, the ribs 100may terminate below the top surface 104 of the screw in the same mannerdescribed previously or may extend fully to the top surface 104 asshown. Further variations may be employed in the location and number ofribs such as suggested in FIG. 47 in which a plurality of spacedparallel ribs 100, are formed on the sidewall 102. Similarly, as shownin FIG. 48 the ribs 100' may be formed on the back out wall 106 ifdesired. In this regard it may be noted that in the three-groovedvariant of this type of recess, the back out wall 106 of each groove 96is longer than the drive wall 102 of the groove in that the moreinwardly disposed portions 108 of the back out wall also serves todefine the central portion 98 of the recess, the innermost end 108 ofthe back out wall 106 merging with the drive wall 102 of the nextadjacent groove. The ribs 100' may be provided on the inner portions,outer portions or both portions of the back out wall 106 as shown inFIG. 48.

The foregoing modifications to the three-grooved recess described may beemployed in connection with a conventional substantially complementarythree-blade driver shown in FIGS. 49 and 50. It may be desirable,however, to modify the driver to enhance further the grip between thedriver and recess and FIGS. 51-55 illustrate various modifications ofthe conventional three-blade driver. As shown, the conventionalthree-blade driver configuration includes a central portion or core 109from which three driving blades 110 extend, generally radially, eachblade 110 having a driving surface 112 and a back out surface 114 whichsubstantially parallel each other and lie along substantially verticalplanes. Each of the blades 110 includes a lower edge 115 at its drivingsurface. The back out wall 114 associated with each blade may beconsidered as having an outer portion 116 which is received in therecess groove and an inner portion 118 which partly defines the core 109of the driver and which fits within and against the inner portion 108 ofthe back out wall 106 of the recess. The lower edge 117 of the innerportion of the back out wall of the driver may be substantiallyhorizontal. The driver may be modified in a manner similar to thatdescribed previously by providing one or more transverse ribs 120 on thedriving face 112 of each blade to dig into and engage the ribs 100 onthe corresponding surfaces of the recess. Alternatively, one or moreribs 122 may be formed on the driving surface 112 of the bladesubstantially parallel to the lower inclined edge 115 and one such rib122 may be located at the lower inclined edge 115 (FIG. 52). A furthervariation is shown in FIG. 53 in which the rib 124 extends from thelower edge 115 of the drive surface substantially continuously along thelower edge 117 of the back out surface of the driver. In a furthervariation the back out wall may be somewhat hollowed out near its loweredge as suggested at 126 in FIGS. 54 and 55 to define a sharp edge 128which may engage firmly the corresponding surface of the recess definingportion of the back out wall on the screw recess. Further variations maybe employed, for example, in which the upper regions of each of thedriving and back out surfaces of the driving blades are provided withsubstantially transversely extending ribs for engagement with thecorresponding surfaces of the recess in a manner similar to thatsuggested in FIG. 16. While it is believed that these will be mosteffective in conjunction with a recess having upwardly extending ribsengageable with the transverse ribs on the driver, the modified driveris believed to increase the effectiveness in retarding the tendency topop out even in the absence of ribs on the recess.

Certain aspects of the invention may be incorporated into other types ofscrew fasteners. For example, FIGS. 56 and 57 show a screw fastenerhaving a protruding head described more fully in U.S. Pat. No. 3,584,667to Reiland. The head includes an upwardly extending driven member 130having generally serpentine peripheral surfaces which are arranged todefine a series of drive walls 132. One or more of the driving wallsurfaces 132 of the member may be provided with upwardly extending ribs134 in substantially the same manner as described herein. The ribs 134preferably are located at those regions of the driving surface where thedriving tool 136 will exert maximum driving torque so that the ribs 134may be deformed to destroy the stick-fit property as the screw istightened.

It should be noted that the embodiments of the invention described withregard to recessed screw head configurations have been described inconnection with flat head screws. The various aspects of the inventionmay be employed with equal effectiveness with other screw headconfigurations including conventionally struck slotted heads. Thevarious recess configurations may be formed by conventional cold headingmachinery. The various recess rib and driver rib configurations may beemployed independently of each other or in various combinations. Therecesses may be employed with conventional drivers or modified driversdescribed herein, as desired.

The various recess configurations described above may be formed byconventional techniques in commercially employed heading machines. FIGS.58 and 59 illustrate a punch of a configuration which is adapted to formthe recess shown in FIGS. 2 and 3. The punch, indicated generally by thereference character 150, may be formed in accordance with conventionalpunch forming techniques. The punch 150 includes a body portion 152having a face 154 and an integral nib 156 which protrudes from the face154. The nib 156 is the complement of the shape of the recess and theface 154 of the punch 150 is of complementary shape to that of theintended screw head, here described for purposes of illustration as aflat head. The nib 156 includes a central core 158 and a plurality ofblades 160 which extend generally radially and outwardly from the core.Each of the blades 160 has a pair of side surfaces 162, 164 and an endsurface 166 which is inclined upwardly and outwardly from the outerregion of the core 158. The blades 160 at their upper ends, merge intothe face 154 of the punch to define an integral structure. The surfaces162 and/or 164 of the blades are provided with grooves 168 which aredefined by groove sidewalls 170. The grooves define a cross-sectionalarea and configuration substantially identical to that of the rib 26which is to be formed on the sidewall of the recess groove. Thus, thegrooves 168 are of the order of a few thousandths of an inch in depth orless and their relative dimensions are exaggerated for clarity in thedrawings. The grooves 168 may be formed on one or more of each of thesurfaces 162 or, on both of the surfaces 162 and 164 as desired. In theillustrated punch the grooves 168 are formed on the surface 162 of eachblade 160 which will define the drive wall 22. More than one such groovemay be formed in order to form recesses having a plurality of ribs asdescribed and as illustrated in FIGS. 47 and 48. The grooves 168 extendfrom the lower edge 172 of the respective blade sidewalls 160 and/or162, where the sidewalls join the end surfaces 166, and extend upwardlyto the extent desired. The grooves may extend fully to the top of theblades 160, where they meet the face 154 of the punch or, may terminatebelow the juncture of the blade 160 and face 154 depending on the ribconfiguration which is to be fabricated. Each of the grooves is formedso that it is symmetrically disposed about a substantially verticalplane (i.e., a plane which parallels the longitudinal axis of the punch,one such plane being shown at 174 in FIG. 58).

FIGS. 60 and 61 illustrate a punch which may be employed to cold formthe recess of the type shown in FIGS. 34, 35 and 36. Here, the punch isprovided with the same general arrangement as described above withregard to FIGS. 58 and 59. This punch, however, is illustrated to showthe configuration of a modified form of groove 176 in which the ribintended to be formed has a ridge 74 (see FIG. 35) which does notparallel the recess sidewall from which it protrudes. Here, the bottomline 178 of the sidewalls 180 of the groove 176 does not extend parallelto the sidewall of the blade although each groove 176 is disposedsymmetrically about a vertical plane 174. The sidewalls 180 may also bein vertical planes in this embodiment.

FIGS. 62 and 63 illustrate a punch for fabricating the recess shown inFIGS. 31 and 32. This punch is provided with a groove 182 extendingalong its intermediate wall 184 which defines in part the punch core 186and which will form the intermediate walls 18 of the recess shown inFIGS. 31 and 32. These grooves 182, as the others defined above, alsoare symmetrically disposed along a substantially vertical plane 174.

In like manner punches may be fabricated to produce recesses ofconfigurations like those shown in FIGS. 9, 23, 24, 39, 40-48 as well asexternal head configurations embodying the invention as suggested inFIGS. 56 and 57. The punch for forming one or more ribs on an externallywrenchable fastener would be defined by a socket corresponding to theshape of the head and provided with one or more grooves extending alongthe side surfaces of the socket. It is believed that the foregoingdescriptions are sufficiently illustrative so that one of ordinary skillin the art may not incorporate the invention in various recessesincluding those illustrated as well as those which are not specificallyshown as, for example, the recesses shown in U.S. Pat. No. 3,237,506.

It should be understood that the foregoing description of the inventionis intended to be illustrative thereof and that other modifications andembodiments of the invention may be apparent to those skilled in the artwithout departing from its spirit.

Having thus described the invention what I desire to claim and secure byLetters Patent is:
 1. A driving tool for engagement with a recess in anend of a screw comprising:a shank portion and a recess-engaging portionformed at an end of said shank portion, said recess-engaging portioncomprising a central core and a plurality of blades radiating from saidcore, said core being defined in part by an intermediate wall extendingbetween each pair of adjacent of said blades; and a rib formed along thelower edge of each of said intermediate walls and extending between eachof said pairs of adjacent blades.
 2. A driving tool as defined in claim1 further comprising:means forming a second rib on each of saidintermediate walls at a location above said first mentioned rib.
 3. Adriving tool for engagement with a recess in an end of a screwcomprising:a shank portion and a recess-engaging portion formed at anend of said shank portion, said recess-engaging portion comprising acentral core and a plurality of blades radiating from said core, saidcore being defined in part by an intermediate wall extending betweeneach pair of adjacent of said blades; and the lower region of each ofsaid intermediate walls being of concave configuration and formed todefine a relatively sharp edge at the lower end of each of saidintermediate walls.
 4. A driving tool as defined in claim 3 furthercomprising:a rib on each of said intermediate walls above said lowersharp edge thereof.
 5. In combination, a screw having a recess at oneend thereof and a driver, mateable with said recess to enable saiddriver to rotatably drive said screw, the improvement comprising:saidrecess including a central portion and a plurality of grooves extendinggenerally radially and outwardly from said central portion, each of saidgrooves being defined at least in part by a pair of sidewalls; aprojection formed on at least one sidewall of each of said grooves, saidprojection extending from its associated sidewall and being ofsufficiently small dimensions as to be deformable in response toapplication of driving torque by said mated driver; said driverincluding a central core portion and a plurality of blades radiatingtherefrom, said blades being equal in number and spacing to the groovesof said recess, each of said blades being defined by a pair of surfaceson opposite sides thereof to face said sidewalls of said grooves whenmated; and means defining a rib on that surface of each of said bladeswhich faces its associated groove sidewall having said projection formedthereon, said ribs being located on said blades and with respect to saidrecess and said sidewall projections so that said ribs and sidewallprojections may engage and interlock with each other.
 6. The combinationas defined in claim 5 wherein said driver is fabricated from a harder,less deformable material than said screw whereby said ribs on said blademay dig into said projections on said groove sidewalls.
 7. Incombination, a screw having a recess formed at one end thereof and adriver mateable with said recess to enable said mated driver torotatably drive said screw comprising:said recess including a centralportion and a plurality of grooves extending generally radially andoutwardly from said central portion, said central portion of said recessbeing further defined in part by intermediate walls extending betweenthe inner regions of adjacent of said grooves; said driver comprising acentral core and a plurality of blades extending from said central core,said blades being equal in number and spacing to the grooves of saidrecess, said core being defined in part by an intermediate wallextending between each pair of adjacent of said blades; and a rib formedalong the lower edge of each of said intermediate driver walls andextending between each of said pair of adjacent blades, said ribs beingengageable with the intermediate walls of said recess.
 8. Thecombination as defined in claim 7 further comprising:said intermediatewall of said recess including an elongate projection formed thereonextending from the lower region of said intermediate recess wallupwardly toward the top of said recess, said elongate projection andsaid rib being disposed so that when said driver and recess are mated,said projection and rib may cross and interlock with each other.
 9. Thecombination as defined in claim 8 further comprising:each of said recesswall projections extending to the top of said intermediate recess walls;said driver including, on each of its intermediate walls, a second ribdisposed above said first mentioned rib, said second mentioned rib beingspaced from said first mentioned rib so that when said driver and recessare mated, said second mentioned rib will be located below the top ofsaid recess and will be in a position to engage and interlock with theupper region of said projection on said intermediate recess wall.
 10. Incombination, a screw having a recess formed at one end thereof and adriver mateable with said recess to enable said driver to rotatablydrive said screw comprising:said recess including a central portion anda plurality of grooves extending generally radially and outwardly fromsaid central portion, said central portion of said recess being furtherdefined in part by walls extending between the inner regions of adjacentof said grooves; said driver comprising a central core and a pluralityof blades extending from said central core, said blades being equal innumber and spacing to the grooves of said recess, said core beingdefined in part by an intermediate wall extending between each pair ofadjacent of said blades; and the lower region of each of saidintermediate walls being defined by a concave region of a configurationto define a relatively sharp edge at the lower end of each of saidintermediate walls.